Coagulation test, which is one type of blood test, is conducted by measuring the clotting time of blood in order to grasp the state of hemostasis mechanism. When prolongation of clotting time is observed, congenital coagulation disorder due to congenital deficiency or abnormality in blood coagulation factors, or acquired coagulation inhibition due to autoantibodies or drugs, e.g. warfarin, that inhibit coagulation reaction is suspected as the cause of the prolongation. Congenital coagulation disorder can be distinguished from acquired coagulation inhibition based on a test (cross-mixing test) that measures the clotting time of a specimen prepared by mixing normal plasma and test plasma (i.e., plasma to be tested) showing prolongation of the clotting time. That is, in the case of congenital coagulation disorder, prolongation of the clotting time is corrected by the test plasma being mixed with normal plasma, but in the case of acquired coagulation disorder, prolongation of the clotting time is not corrected.
With respect to acquired coagulation disorder caused by autoantibodies, it is known that the pathological conditions are different depending on the kinds of the autoantibodies. For example, patients having autoantibodies against blood coagulation factors (also referred to as coagulation factor inhibitors) show bleeding symptoms in general. On the other hand, in the case of an autoantibody called lupus anticoagulant (LA), it inhibits phospholipids that are necessary for phospholipid-dependent coagulation reaction, but patients having LA show thrombus symptoms. Therefore, distinguishing a sample containing a coagulation factor inhibitor from a sample containing LA is clinically important. However, as described above, since both samples show prolongation of clotting time, it is difficult for an ordinary coagulation test to distinguish them from each other. Thus, for this distinction, it is necessary to separately conduct a test or the like that detects coagulation factor inhibitors or LA.
On the other hand, in recent years, for assessment of the entire process from the start of clotting to formation of fibrin clots, analysis of clot waveform has been attracting attention. The clot waveform is a waveform that represents temporal change in optical characteristics such as transmission and scatter of light in the sample, the change occurring in accordance with advancement of blood sample clotting. Through the analysis of the clot waveform, information such as velocity and acceleration of coagulation is obtained. For example, US2003/0104493 describes that patients having antiphospholipid antibodies (including LA) and receiving warfarin showed maximum coagulation acceleration and maximum coagulation deceleration that are different from those of healthy individuals. A document titled “Towards standardization of clot waveform analysis and recommendations for its clinical applications”, by Shima M. et al., J Thromb Haemost, 2013, vol. 11, p. 1417-1420 describes the following: clot waveform analysis was conducted on acquired hemophilia A, which is a disease in which the activity of factor VIII is decreased by factor VIII inhibitor; and it was found that samples derived from acquired hemophilia A are characterized by their lower values of maximum coagulation velocity and maximum coagulation acceleration than those of normal samples.